Relative to planar MOS structures, new generations of three-dimensional fin-type field effect transistors (FinFETs) have been actively developed following the trend of scaling down the size of the semiconductor devices. As the gate electrode is often located above the channel region for the planar transistor, the gate electrode wrapping around the channel from three sides in FinFETs provides better electrical control over the channel. While the size of the semiconductor device keeps decreasing, the fin arrangement becomes tightened and the gate pitch is reduced.